1. Field of the Invention
The present invention relates to an apparatus for demodulating an AM data multiplexed modulated wave signal generated by an AM data multiplexing and modulating apparatus, to thereby obtain a baseband digital signal. More particularly, the invention relates to an apparatus for demodulating an AM data multiplexed modulated wave signal and deriving therefrom a baseband digital signal which wave signal is obtained through AM data multiplexing and modulating as the present inventor has proposed, by amplitude modulating a carrier having a frequency fc with an analog signal by an AM type modulator to multiplex digital modulated signals at frequency positions of (fc+f.alpha.) and (fc-f.alpha.) line symmetrical to the carrier having the frequency fc on the frequency axis.
2. Description of the Related Art
Conventional apparatuses for demodulating a data multiplexed modulated wave signal are classified mainly into time division multiplexing and frequency division multiplexing. For time division multiplexing, data is picked up by selecting a data multiplexed time, and for frequency division multiplexing, data is picked up by a data multiplexed frequency band.
However, an AM data multiplexed modulated wave signal, which is obtained through AM data multiplexing and modulating by amplitude modulating a carrier having a frequency fc with an analog signal by an AM type modulator to multiplex digital modulated signals at frequency positions of (fc+f.alpha.) and (fc-f.alpha.) line symmetrical to the carrier having the frequency fc on the frequency axis, has the AM type modulated components and data modulated components multiplexed in the same frequency band and at the same time. It is impossible to pick up desired data by selecting a data multiplexed time or a data multiplexed frequency band.